BQ25886: Compatibility with commercial power bank

Hi Stefano

Do you have a schematic of your circuit that you can share with me for review?

During the condition with power bank batteries more discharged and you see the problem, how low is the power bank voltage?

Hi Bill,

I have not a schematic because we are checking the architecture of the system that you can see in below picture:

The discharged battery are the the electronic lock battery (5,7 V ) that is charged by  BQ25886; the power bank is charged.
When I connect the power bank the BQ start the charge with precharge value of 30mA to the battery.

The current requested by the power bank is around 40mA and this value of output current is too low for power bank and the protection circuit od the power bank disconnect the output; for the power bank is a typical working behavioure.

Thnk you for your suggestion.

BR
Stefano 

Hi Stefano

Is the BQ25886 entering DPM due to low input voltage (4.3V)?

What is the Input current limit setting, ILIM pin 8?

Hi Bill,
About first issue:

- The battery connected to the BQ is completely discharged and the coltage is 5,7V
- I connect the power bank and the BQ start che precharge at 1/10 of ICHARGE (Iprecharge=30mA=
- In this condition the power bank current is 40mA 
- After 30 sec the power bank disconnect the output and enter in hidle, in this condition the output voltage of the power bank is 2,5V

About second issue:

- the BQ is charging the battery and the charge current is decreasing 
- the BQ charging termination is 30mA but when the input curren is below 40 mA (35 mA of charge current) the power bank disconnect the output voltage.
- the output voltage of the power bank is 2,5V and the BQ do not terminate the charge

The ILIM is 500mA

Regards

Stefano 

Hi Stefano

Thanks for the additional information.  

Both problems appear to be during a low output current condition from the power bank.  During Precharge and Termination the power bank output will disconnect.

Is this problem only occurring with this one model of power bank, do you have others that work?

If you increase system load, more load on power bank does this prevent the drop out?

Hi Bill,

Bill Johns said:

Is this problem only occurring with this one model of power bank, do you have others that work?

Yes I've check other power bank and the beavioure is similar; the ony difference is the current where the ouput is disabled and the other is higher. This beavioure is also confirmed by your app.note SLVA770.

If I increase the power consumption, I will decrease the charged life of the battery pack

My question is how did they solve this problem in the cell phone, especially for the premature disconnection in the final recharge.

BR

Stefano

Hi Stefano

This is going to be difficult; the problem is with power bank not he BQ25886.

If you have a way to turn on the system load on periodically when power bank is connected this could be enough to keep the power bank active.